Adhesive, waterproof and hydrolysis-resistant bonding layer for metal, ceramic, glass, polymer-plastic bonds and dispersion for producing it

ABSTRACT

A dispersion for producing an adhesive, waterproof and hydrolysis-resistant bonding layer for bonding metal, ceramics, glass and for polymer-plastic bonds, including a phenol resin-methacrylate dispersion containing phenol with free methylol groups, one or more mono- or multifunctional methacrylate compounds, dispersed acrylate, water and acetone.

The invention relates to an adhesive, waterproof hydrolysis-resistantbonding layer for metal, ceramic, glass, and polymer-plastic bonds and adispersion for producing it. The bonding layer of the invention ispreferably used for bonds which are exposed to steady mechanical andtemperature-change stresses, along with simultaneous moisture action, inthis case for bonds in dental technology in particular.

Numerous suggestions for bonding plastics with metal surfaces in agapless manner have been made in the past years. The basic principle ofthese processes is that in a first step an inorganic (mostly silicate)layer is applied to a metal surface (silicate treatment) and that in asecond step the surface is coated with a functional alkoxysilane (silanetreatment). In this case the adhesive silane (mostly hydrolizedγ-methacryloyloxypropyltrimethoxysilane) constitutes the bond betweenthe inorganic silicate layer and a methacrylate-containing plasticdental material, wherein on the one hand the free OH groups of theadhesive silane, with the surface OH groups of the silicate layer, arechemically bonded to the silicate layer in the course of condensationreactions while, on the other hand, there is bonding to a plastic dentalmaterial for example, via the methacrylate group of the adhesive silane.The known processes are distinguished by the methods of the differentapplication of the silicate layer, while the application of the adhesivesilane is almost identical in all described processes.

U.S. Pat. No. 4,364,731 describes a process for applying a silicondioxide layer to metallic denture parts for a high-frequency magnetronsputtering device. Since a vacuum coating installation is required forthis, the process requires a considerable outlay for apparatus.

In DE-PS 34 03 894 the application of the silicate layer takes place bymeans of a clearly more simple flame-hydrolysis process of thetetraethoxysilane whereby, however, good adhesion of the plastic to themetal is only attained when the apparatus parameters are strictlyadhered to.

Furthermore, a process is described in DD 276 453 in which asilicate-chromium oxide layer is applied to a dental alloy surface bymeans of a sol-gel solution and is fixed by means of a subsequenttempering process (320° C., 2 to 8 min). Dental alloys with an increasedcopper content (>5% of mass) in particular reveal themselves as beingcritical, because in this case copper(II)-oxide, which does not adherewell to the alloy surface, is formed by the tempering process, becauseof which the metal-plastic bond is weakened.

A method is described in DE-PS 38 02 043 in which the silicate layer isapplied in a sand-blasting process by adding a defined amount of silicondioxide of a mean particle size ≦5 μm to the abrasive corundum. In thecourse of this, local energy densities appear in the impact area of thecorundum particles, which are sufficient to fuse the fine silicateparticles to the metallic surface. With this process, too, sufficientbonding adhesion can only be achieved with the most scrupulous adherenceto the operating parameters.

The known described processes all require an expensive outlay inapparatus or chemicals and several process steps. In addition, when usedin the dental field, the Si-O-Si bonds of the silicate layer aresubjected to continuous hydrolysis attack because of the constantexposure of the plastic-metal bonds to moisture in the mouth area, whichcan result in a weakening of the bond adhesion during prolongedexposure.

Thus it is the object of the invention to recite an adhesive, waterproofand hydrolysis-resistant layer which can be produced with little outlayin apparatus and which is suitable for bonding plastics, in particularmethacrylate-containing plastic dental materials or adhesives, in adurable manner with a high degree of adhesiveness and free of edge gapsto metal, glass, ceramic or organic surfaces.

The object of the invention is attained by the means recited in thecharacterizing parts of the claims.

A dispersion is used for making the bonding layer which in accordancewith the invention consists of a phenol-formaldehyde dispersion (inaddition to phenol as the initial monomer, it is of course also possibleto use phenol derivatives, such as cresylol and resorcinol as reactionpartners) with hydroxymethylated phenol with free methylol groups,polyvinyl formal or polyvinyl butyral as plasticizing component,dispersed acrylate, distilled water and acetone. One or several mono- ormultifunctional methacrylate compounds such as urethane methacrylatesand hydroxy methacrylates are added to this dispersion. Thesepolymerizable, olefinically unsaturated monomers can also bealkoxysilanes with at least one polymerizable olefinically unsaturatedgroup, such as 3-glycidoxypropyltriethoxy silane,aminothylaminopropyltrimethoxy silane, methacrylicacid-3-trimethoxysilylpropyl ester or vinyltrimethoxysilane. Thealkoxysilane can have one, two or three methoxy or ethoxy groups and onefunctional organic group. In particular, a phenol resin dispersion to beused for the invention contains, in relation to 100 ml dispersion, 0.5to 5 g phenol resin and phenol with free methylol groups, 0.05 to 0.5 gof polyvinyl formal or polyvinyl butyral, 1 to 5 g dispersed acrylate,10 to 30 ml distilled water and 10 to 30 ml acetone, wherein the amountof phenol with free methylol groups is 0.05 to 0.2% of the mass inrelation to the dispersion. 2 to 20 g of one or several mono- ormultifunctional methacrylate compounds are added to this dispersion, sothat the result is a phenol resin-methacrylate dispersion of theinvention. This dispersion is applied to a metal, glass, ceramic ororganic surface and subjected to a heat treatment at between 120° to220° C. In the course of this the methylolphenols condense via theA-stage and B-stage resins finally through spatially cross-linkedC-stage resins to form the bonding layer of the invention. Themethacrylate monomers can be linked by means of base-catalytic additionreactions of the methylene group of the methacryl monomer to thecarbonyl function of the aldehyde (aldol addition) or bonded byinterpenetrating linkages to this phenol resin space network. Thedispersion has a pH of 7.2 to 8.

The attainment of the object of the invention has the followingadvantages over the state of the art:

The applied coating prevents the diffusion of water which weakens thebonding of a plastic or an adhesive to a surface of a metal alloy, forexample.

The solidification of the coating takes place in a relatively lowtemperature range (120° to 220° C.), so that there are no discolorationsor scale formations, for example on critical dental alloys.

The attainment of the object of the invention is completely independentof the bonding materials which are to be brought into contact.

No additional adhesive agent is required with the attainment of theobject of the invention, because the molecules of the adhesive agenthave already been integrated in the bonding layer.

The attainment of the object of the invention can be realized withlittle outlay for apparatus, such as simple heat sources, and withoutproblems in any area of use without the necessity of expensive adherenceto process parameters.

Advantageous embodiments of the invention, particularly its use indental technology, ensue from the dependent claims and will be describedin detail in the following exemplary embodiments which do not limit theinvention.

The subsequently cited tension or pressure shear strength values ofmetal-plastic bonds or metal-metal adhesions are used to demonstrate theattainment of the object of the invention without being in a position todescribe the type of the adhesion mechanism which occurs, because inthis case explanations of the adhesions used up to now need to berevised.

The unconditioned surface is used as a comparison value (blank value) ofthe bonding strength, wherein this surface as well as the surfaces usedfor the invention are first sand-blasted (aluminum corundum 50 to 250μm, 1 to 5 bar). A further comparison value is the adhesive strengthwhich is achieved if the surfaces of the solid bodies are coated withonly a portion of the dispersion in accordance with the invention(Dispersion A), and finally as the third comparison value the shearstrength which can be achieved with the dispersion of the invention.

Composition of the Dispersion A:

0.75 g phenol resin and phenol with free methylol groups

0.1 g polyvinyl formal or polyvinyl butyral

2 g dispersed acrylate

20 ml distilled water

60 ml isopropanol

20 ml acetone

To obtain the composition of the invention (Dispersion B), the followingwas added to 100 ml of this dispersion, the content of phenol with freemethylol groups of which is 0.1% of mass:

2 g methacrylic acid-3-trimethoxysilylpropyl ester

5 g methylmethacrylate

2 g triethyleneglycoldimethacrylate

1 g 2,4-butandioldimethacrylate

1 g trimethylolpropanetriacrylate

0.1 g camphor quinone

0.2 g triethanolamine

In the example, this dispersion as well as the dispersion A forproviding the said comparison values by itself, are applied tosand-blasted dental alloys and are subjected to a heat treatment at 120°to 220° C., preferably 150° C., for approximately 15 minutes. It isfurthermore possible to apply to this surface a light-hardeningopaqueing agent on a methacrylate basis and to polymerize it. Followingthis, a cylinder (in the example with a diameter of 5 mm and height of 2mm) of light-hardening plastic is formed and also polymerized. In thiscase it is advantageous to add to the dispersion of the invention 0.1 to1% by mass of photo-active components, such as the system of camphorquinone and triethanolamine or N,N-dimethylaminoethylmethacrylate or thelike, which results in further adhesion improvement. The metal-plasticbonds made in this way are boiled for one hour in distilled water, arestored in water for 24 h and are subsequently tested for bondingstrength in a pressure shear test (feed speed 1 mm min⁻¹). The bondingstrength values obtained are shown in Tables 1 and 2.

                  TABLE 1                                                         ______________________________________                                        Metal-Plastic Bond (Plastic: Dentacolor)                                      ______________________________________                                                 Shear Strength                                                                            Shear Strength                                                                            Shear Strength                               Dental Alloy                                                                           Blank value Dispersion A                                                                              Dispersion B                                 ______________________________________                                        Maingold 11      MPa     12    MPa   16    Mpa                                Degulor  10.5    MPa     11    MPa   15.5  MPa                                Palliag  9       MPa     11    MPa   18    MPa                                Auropal 2                                                                              10.8    MPa     11.2  MPa   16.5  MPa                                Duo Pal 6                                                                              8.8     MPa     10.4  MPa   16.5  MPa                                Simidur  7.9     MPa     10.2  MPa   16.9  MPa                                Wiron 88 7.2     MPa     9.5   MPa   15.3  MPa                                ______________________________________                                        "DENTACOLOR" has the following physical properties:                                                 Average                                                 Physical properties   values                                                  ______________________________________                                        Compressive strength  392 MPa                                                                       55740 psi                                               Flexural strength DIN 13922                                                                         68 N/mm.sup.2                                                                 68 MPa                                                                        9667 psi                                                Vickers hardness (HV 0.3)                                                                           350 N/mm.sup.2                                          after 24 hours                                                                in water of 37° C.                                                                           56880 psi                                               Water absorption      0.7% by weight                                          Color stability test  Complies with                                           (UV-light/heat) DIN 13922                                                                           standard                                                Total filler content  approx. 72.0%                                                                 by weight                                               Inorganic filler content                                                                            approx. 51.0%                                                                 by weight                                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Metal-Plastic Bond (Metal: Wiron 88)                                                   Shear Strength                                                                            Shear Strength                                                                            Shear Strength                               Dental Alloy                                                                           Blank value Dispersion A                                                                              Dispersion B                                 ______________________________________                                        P 50     15.4    MPa     16.7  MPa   28.5  MPa                                Estilux  15.1    MPa     16.8  MPa   26.8  MPa                                Visio-Molar                                                                            13.4    MPa     15.2  MPa   25.6  MPa                                Charisma 12.1    MPa     14.8  MPa   23.2  MPa                                Heliomolar                                                                             11.2    MPa     12.5  MPa   19.5  MPa                                ______________________________________                                         "WIRON 88" has the following composition based on mass %: 64% Ni, 24% Cr,     10.0% Mo, 1.5% Si and 0.5% Ce.                                           

In addition to the metal-plastic bonds shown in Tables 1 and 2, thetension shear strength values shown in Table 3 are used to further provethe success of the invention. Conditioning of the metal surface tookplace analogously to the process already described in connection withthe production of the metal-plastic bonds. The length of overlap of theglued spot in this case is 10 mm and the glued area 50 mm². These gluedpieces were boiled for 10 hours.

                  TABLE 3                                                         ______________________________________                                        Metal-Metal Adhesion (Metal: Wiron 88)                                                 Shear Strength                                                                            Shear Strength                                                                            Shear Strength                               Adhesive Blank value Dispersion A                                                                              Dispersion B                                 ______________________________________                                        Chemiace 12.8    MPa     14.5  MPa   28.5  MPa                                Brilliant                                                                              14.4    MPa     16.3  MPa   25.2  MPa                                Enamel Kit                                                                    Palavit 55                                                                             12.1    MPa     13.8  MPa   25.4  MPa                                Microfill                                                                              11.2    MPa     13.2  MPa   20.8  MPa                                pontic                                                                        Helapox blue                                                                           9.5     MPa     20.2  MPa   19.5  MPa                                ______________________________________                                    

In a comparison between the methacrylate-containing dental adhesivesChemiace, Brilliant enamel kit, Palavit 55 and Microfill pontic, Helapoxblue (epoxy resin) takes up a certain special position.

The tension shear strength of the metal-metal adhesions as well as thepressure shear strength of the metal-dental plastic bonds show that withthe solution in accordance with the invention an approximately 100%higher adhesive strength can be attained in comparison to unconditionedsurfaces. The break is a pure cohesion break. An adhesive, water-proofand hydrolysis-resistant bonding layer is available by means of theinvention which is suitable for the most diverse bonds and is thereforenot limited to application in dental technology. A use of the dispersionof the invention, which is also advantageous as a lacquer base coat, isprovided in machine and autobody construction, by means of which a clearincrease in the life of the bonding layer system can be achieved evenunder tropical conditions.

I claim:
 1. A dispersion for producing an adhesive, waterproof andhydrolysis-resistant bonding layer for bonding metal, ceramics, glassand for polymer-plastic bonds, comprising a dispersed phenol resincontaining phenol with free methylol groups, one or more mono- ormultifunctional methacrylate compounds, dispersed acrylate, distilledwater and acetone.
 2. The dispersion in accordance with claim 1, whichcomprises 100 ml of a phenol resin dispersion, which contains 0.5 to 5 gphenol resin containing phenol with free methylol groups, 0.05 to 0.5 gof polyvinyl formal or polyvinyl butyral, 1 to 5 g dispersed acrylate,10 to 30 ml distilled water and 10 to 30 ml acetone, and 2 to 20 g ofone or more mono- or multifunctional methacrylate compounds.
 3. Thedispersion in accordance with claim 1, wherein the methacrylatecompounds are selected from the group consisting of urethanemethacrylates and hydroxy methacrylates.
 4. The dispersion in accordancewith claim 1, which further comprises an alkoxysilane.
 5. The dispersionin accordance with claim 4, wherein the the alkoxysilane has three, twoor one methoxy or ethoxy group and at least one functional organicgroup.
 6. The dispersion in accordance with claim 5, wherein thefunctional organic group of the alkoxysilane is a vinyl, methacrylate oran epoxy group.
 7. The dispersion in accordance with claim 6, whereinthe alkoxysilane is selected from the group consisting ofvinyltrimethoxy silane, methacrylic acid-3-trimethoxysilylpropyl ester,3-glycidoxypropyltriethoxy silane and aminoethylaminopropyltrimethoxysilane.
 8. The dispersion in accordance with claim 1, which furthercomprises 0.1 to 1% of mass of one or more photo-active components inrelation to the mass of the methacrylate compounds.
 9. The dispersion inaccordance with claim 8, wherein the photo-active component is aphoto-active system of camphor quinone and triethanolamine orN,N-dimethylaminoethylmethacrylate.
 10. The dispersion in accordancewith claim 1, wherein the dispersion has a pH value between 7.2 and 8.11. An adhesive lacquer bonding layer for use in machine and autobodyconstruction, produced by heat treating for hardening a lacquer basecoat comprising a dispersed phenol resin containing phenol with freemethylol groups, dispersed acrylate, water, acetone and one or moremono- or multifunctional methacrylate compounds.
 12. A lacquered bodycomprising a substrate having bonded thereto an adhesive bonding layerin accordance with claim 11, wherein the lacquer base coat is hardenedby a heat treatment at a temperature from 120° to 220° C., and one ormore lacquer coats are attached to the resultant hardened lacquer basecoat.
 13. The dispersion in accordance with claim 1, wherein the phenolwith free methylol groups is contained in an amount of 0.05 to 0.2% ofthe mass of the dispersion.
 14. The dispersion in accordance with claim2, and which further comprises 1 to 10 g of an alkoxysilane having oneto three methoxy or ethoxy groups and at least one functional organicgroup.
 15. The dispersion in accordance with claim 4, which includes thefollowing two portions:(a) a phenol resin containing phenol with freemethylol groups, polyvinyl formal or polyvinyl butyral, dispersedacrylate, distilled water, isopropanol and acetone; and (b) methacrylicacid-3-trimethoxysilylpropyl ester, methylmethacrylate,triethyleneglycoldimethacrylate, 2,4-butandioldimethacrylate,trimethylolpropanetriacrylate, camphor quinone andtriethanolamine,wherein the phenol with free methylol groups beingcontained in an amount of 0.1% by mass of the dispersion.